Elucidation of the genetic regulation of the diversification of embryonic cell populations into multiple distinct derivatives sub-serving specialized functions is a central issue in developmental biology. The neural crest is a transient embryonic population of precursor cells that gives rise to a diverse array of cellular derivatives including neurons and glia of the peripheral nervous system, pigment cells and elements of the craniofacial skeleton, among others. Similarly, hematopoietic progenitors derived from lateral plate mesoderm ultimately generate multiple blood cell types including erythroid, myeloid and lymphoid derivatives as well as cells of the vasculature. Although both neural crest and hematopoietic lineages have been studied extensively, elucidation of the genetic regulation of the diversification of these lineages remains incomplete. The major goals of this proposal are to provide new insights into the genetic regulation of the generation of neural crest and hematopoietic precursors and the specification and development of distinct neural crest and hematopoietic subpopulations. We will determine the functions of critical regulators of the development of both lineages and elucidate the genetic pathways and networks that underlie cell diversification. We will utilize zebrafish mutants that display specific and severe defects in hematopoiesis and/or neural crest development. We propose a research plan comprised of inter-related experimental approaches to analyze the contributions of known critical regulatory genes and genes corresponding to these mutant loci in the genetic regulation of neural crest development and hematopoiesis. We will systematically assess the roles of these genes in the generation of neural crest and hematpoietic progenitors, the specification and development of developmentally distinct sublineages and the generation of differentiated cells types derived from these progenitors. These analyses will determine the roles of these genes in regulating cell survival and/or providing instructional cues required for the cellular diversification of these lineages. Additionally, our results will further define unique and overlapping functions of key genetic regulators of neural crest development and hematopoiesis and also identify genes critical for the development of cells derived from both ectoderm (neural crest) and mesoderm (hematopoiesis). We expect that the results of these studies will provide significant new insights into the mechanisms that regulate neural crest development and hematopoiesis specifically, and embryonic cell diversification generally. In addition, because miscues during neural crest development and hematopoiesis result in numerous clinically relevant conditions in humans, our results are likely to provide information leading to the development of strategies for the diagnosis and treatment of human diseases.